Japanese Unexamined Patent Application Publication No. 2003-61207 discloses an example of a work vehicle that charges a battery with regenerative power of an electric motor for driving a propelling device. The electric motor or motor generator drives a pair of front wheels, and the battery supplies the electric motor with electric power. The work vehicle further includes an engine for driving a pair of rear wheels. The electric motor also acts as a power generator for charging the battery with regenerative power of the electric motor while the vehicle is running.
In this vehicle, when regenerative power of the electric motor varies with rotation speed of the electric motor, regenerative power of the electric motor supplied to the battery also varies. Thus, it is difficult to stably supply regenerative power of the electric motor to the battery, and to estimate the time required for charging the battery.
There is a growing demand for a work vehicle which supplies regenerative power of the electric motor to the battery in a stable manner and easily estimates the time required for charging the battery.